Multicarrier DS - CDMA : A Multiple Access Scheme for

In this article we identify some of the key problems that may be encountered when designing a broadband multiple access system with bandwidth on the order of tens or even hundreds of megahertz. We commence with a comparative discussion in terms of the characteristics of three typical code-division multiple access schemes: single-carrier directsequence CDMA (SC DS-CDMA), multicarrier CDMA (MC-CDMA), and multicarrier DSCDMA (MC DS-CDMA). Specifically, their benefits and deficiencies are analyzed when aiming to support ubiquitous communications over a variety of channels encountered in indoor, open rural, suburban, and urban environments. It is shown that when communicating in such diverse environments, both SC DSCDMA and MC-CDMA exhibit certain limitations that are hard to circumvent. By contrast, when appropriately selecting the system parameters and using transmit diversity, MC DSCDMA becomes capable of adapting to such diverse propagation environments at a reasonable detection complexity. Multicarrier DS-CDMA: A Multiple Access Scheme for Ubiquitous Broadband Wireless Communications